From e7d61bd982e4be3e4a2605af07febae953d7c0b3 Mon Sep 17 00:00:00 2001
From: Andrew Kent <andmkent@indiana.edu>
Date: Wed, 14 Jan 2015 15:32:34 +0530
Subject: [PATCH] fixed struct field updates

---
 .../typed-racket/typecheck/tc-envops.rkt        | 16 ++++++++++------
 typed-racket-test/succeed/struct-update.rkt     | 17 +++++++++++++++++
 2 files changed, 27 insertions(+), 6 deletions(-)
 create mode 100644 typed-racket-test/succeed/struct-update.rkt

diff --git a/typed-racket-lib/typed-racket/typecheck/tc-envops.rkt b/typed-racket-lib/typed-racket/typecheck/tc-envops.rkt
index 3b9e95e4..6b2e9649 100644
--- a/typed-racket-lib/typed-racket/typecheck/tc-envops.rkt
+++ b/typed-racket-lib/typed-racket/typecheck/tc-envops.rkt
@@ -46,12 +46,16 @@
      ;; a polymorphic field. Because subtyping is nominal and accessor 
      ;; functions do not reflect this, this behavior is unobservable
      ;; except when an a variable aliases the field in a let binding
-     (build-type make-Struct nm par
-                 (list-update flds idx (match-lambda
-                                         [(fld: e acc-id #f)
-                                          (make-fld (update e ft pos? rst) acc-id #f)]
-                                         [_ (int-err "update on mutable struct field")]))
-                 proc poly pred)]
+     (let/ec abort
+       (make-Struct nm par
+                    (list-update flds idx (match-lambda
+                                            [(fld: e acc-id #f)
+                                             (let ([ft* (update e ft pos? rst)])
+                                               (if (Bottom? ft*)
+                                                   (abort ft*)
+                                                   (make-fld ft* acc-id #f)))]
+                                            [_ (int-err "update on mutable struct field")]))
+                    proc poly pred))]
 
     ;; otherwise
     [(t '())
diff --git a/typed-racket-test/succeed/struct-update.rkt b/typed-racket-test/succeed/struct-update.rkt
new file mode 100644
index 00000000..8650dd69
--- /dev/null
+++ b/typed-racket-test/succeed/struct-update.rkt
@@ -0,0 +1,17 @@
+#lang typed/racket/base
+
+;; ensures updates to a struct's field
+;; which results in Bottom
+;; properly propogates Bottom up
+
+(define-type ABC (U 'a 'b 'c))
+
+(define-struct ABCWrapper ([abc : ABC]))
+
+(: abc-123-let (ABCWrapper -> (U 1 2 3)))
+(define (abc-123-let wrapper)
+  (let ([abc (ABCWrapper-abc wrapper)])
+    (cond
+      [(eq? abc 'a) 1]
+      [(eq? abc 'b) 2]
+      [(eq? abc 'c) 3])))
\ No newline at end of file